Glider observations of sediment resuspension during storm conditions

Abstract

<p>Sediment resuspension and transport on continental shelves are primarily driven by episodic energetic events, such as storm. Unfortunately, resuspension processes remain poorly quantified using traditional sampling techniques due to the intermittency and the intensity of these events. The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increase the probability of capturing sporadic meteorological events. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload and a RDI 600 kHz phased array ADCP to examine storm-induced sediment resuspension in the Gulf of Lion’s shelf (NW Mediterranean). Observations show that early in the storm, when the waves are highest, resuspension is limited by stratification. During the storm, erosion of the pycnocline through thickening of the bottom and surface mixed layers lead to resuspension in the full water column. Coincident optical and acoustic backscatter measurements indicate that the resuspended particulate assemblage is homogeneous and composed of large particles. Glider-ADCP observations showed for the first time that waves may be the predominant forcing which drive the resuspension on the outer shelf (> 80 m) during the winter storm. While, in the Gulf of Lions, which is considered as a relatively low energy continental shelf, modeling studies consider that only current drive resuspension in the outer shelf. This study highlights the usefulness of glider-ADCP to describe episodic processes and to support validation and improvement of regional hydrodynamic models.</p>